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APPENDIX I
SI AND ENGLISH UNITS AND CONVERSION FACTORS
The International System of Units (Syste´me International d’Unite´s, or SI) recognizes seven basic units from which all others are derived. They are:
No. Quantity Name of Unit Symbol
1 length meter m
2 mass kilogram kg
3 time second s
4 electric current ampere A
5 temperature kelvin K
6 luminous intensity candela cd
7 amount of substance mole mol
Multiples of units are designated by the following names:
Amount Prefix Symbol Amount Prefix Symbol
101 deca da 10⫺1 deci d
102 hecto h 10⫺2 centi c
103 kilo k 10⫺3 milli m
106 mega M 10⫺6 micro
109 giga G 10⫺9 nano n
This appendix presents the SI and English (imperial) units, which are used in various areas of trans- portation engineering, and their conversion factors. Some metric units and factors that are not listed in the SI but are commonly used and remain internationally recognized are also included. Examples are the units of centimeter (10⫺2m), hour (3.6⫻ 103s) and kilowatt-hour (3.6 MJ) and multiples of 10, 102, 10⫺1, and 10⫺2.
Urban Transit Systems and Technology. Vukan R. Vuchic
Copyright2007 John Wiley & Sons, Inc. ISBN: 978-0-471-75823-5
For more extensive coverage of units, the following book is suggested:
Cardarelli, Francois. Scientific Unit Conversion. New York: Springer-Verlag, 2003.
Units and conversion factors within and between the two systems of measures are presented here for each dimension in a separate box. The format followed for each dimension is shown in the first box:
millimeter (mm) centimeter (cm) meter (m) kilometer (km)
103mm = 102cm = 1 m 103m = 1 km
LENGTH
inch (in. ") foot (ft. ') yard (yd) mile (mi)
36 in. = 3 ft = 1 yd 5280 ft = 1760 yd = 1 mi 25.40
0.0394 0.3048 3.281 0.9144 1.094 1.609 0.6214
mm in.
m ft
m yd
km mi
SI unit (symbol)
DIMENSION
English unit (symbol) Conversion factors
(for conversion in the direction of the arrow, multiply by the number provided)
square millimeter (mm2) square centimeter (cm2) square meter (m2) hectare (ha) square kilometer (km2)
106mm2= 104cm2= 1 m2 106m2= 102ha = 1 km2
AREA
square inch (in2) square foot (ft2) square yard (yd2) acre
square mile (mi2) 1296 in.2 = 9 ft2 = 1 yd2 3,097,600 yd2= 640
acres = 1 mi2 6.452
0.1550 0.0929 10.76 0.8361 1.196 0.4047 2.471 2.590 0.3861
cm2 in.2
m2 ft2
m2 yd2
ha acre
km2 mi2
cubic millimeter (mm3) cubic centimeter (cm3or cc)
liter (L)
cubic meter (m3)
106mm3= 103cm3= 1 L 106cm3 = 103L = 1 m3
VOLUME
cubic inch (in.3) quart (qt) gallon* (g) cubic foot (ft3) cubic yard (yd3)
46,656 in.3 = 27 ft3 = 1 yd3 4 qt = 1 gal = 231 in.3 1 qt = 57.75 in.3 16.39
0.0610 3.785 0.2642 0.0283 35.32 0.7646 1.308
cm3 in.3
L gal
m3 ft3
m3 yd3
gram (g) kilogram (kg)
(metric) tone or tonne (t)
103g = 1 kg 103kg = 1 t
MASS
ounce (oz)
pound (lb), pounds mass (lbm)
(short) ton (tn+or stn), long ton (ltn)
16 oz = 1 lb 2000 lb = 1 tn
2240 lb = 1.12 tn = 1 ltn 28.35
0.0353 0.4536 2.205 0.9072 1.102 1.016 0.9842
g oz
kg lb
t tn
t ltn
grams/cubic centimeter (g/cm3)
grams/liter (g/L) kilograms/cubic meter
(kg/m3)
103kg/m3= 103g/L = 1 g/cm3
DENSITY
ounces/cubic inch (oz/in.3) pounds/cubic inch (lb/in.3) pounds/cubic foot (lb/ft3) 16 oz/in.3 = 1 lb/in.3=
1728 lb/ft3
1.743 0.5737 16.02 0.0624 0.5933 1.686 cm3
m3 L
ft3 gal in.3
meters/second (m/s) kilometers/hour (km/h)
10 m/s = 3.6 km/h
SPEED
feet/second (ft/s) miles/hour (mph)
88 ft/s = 60 mph (exact) (1.1467 ft/s = 1 mph) 0.3048
3.281 1.609 0.6214
m/s ft/s
km/h mph
meters per second squared (m/s2)
(km/h/s is not used)
g = 9.807 m/s2
ACCELERATION
feet per second squared (ft/s2) miles per hour per second
(mphps) g = 32.18 ft / s2 1 mphps = 1.467 ft/s2 0.3048
3.281 0.4470 2.237
m/s2 ft/s2
m/s2 mphps
meters per second cubed (m/s3)
JERK
feet per second cubed (ft/s3)
Factors are the same as the corresponding ones for acceleration.
dyne (dyn) newton (N) kilonewton (kN)
(metric) ton or tonne (t) (not in SI)
108dynes = 10 N = 1 kN Force = mass ⫻ acceleration 1 N = 1 kg m/s2
FORCE, WEIGHT
ounce (oz) pound force (lbf) 103pounds (kip)
(short) ton force (tnf or s.tnf ) 3200 o
Force = weight ⫻ acceleration gravity const. (gc)
lbf – s2 gc= 32.18 lbm – ft
z = 2000 lbf = 1 tnf
4.448 0.2248 8.896 0.1124
N lbf
kN tnf
pascal (Pa)
kilogram force per square meter (kgf/m2) 1 kgf/m2 = 9.807 Pa
PRESSURE*
LINEAL MASS*
pounds force per square inch (lbf/in.2) (psi) pounds force per square foot (lbf/ft2)
(C) liters per 100 kilometers (L /100 km)
(C) joules per kilometer (J/km)
(E
*Often used for area weight of vehicles.
) kilometers per liter (km/L)
FUEL CONSUMPTION (C) AND EFFICIENCY (E)*
(C) gallons per mile (gpm, gal/mi) (C) British thermal units
per mile (Btu/mi) (E) miles per gallon
(mpg, mi/gal) 0.4251
2.352 235.2 0.00425 0.6557⫻ 103 1.525⫻ 10-3
m/s ft/s
km/h mph
6,894.76 1.45 ⫻ 10–4
47.88 0.02089
Pa psi
Pa lbf/ft2
kilograms per meter (kg/m) pounds per yard (lb/yd)
*Common use in transportation: mass of rails.
0.4960 2.016
kg/m lb/yd
km/h mph
erg joule (J)
107ergs = 1 J
ENERGY
British thermal unit (BTU) foot-pound force (ft-lbf)
1 Btu = 779.2 ft-lbf = 118.98 hp-h 1055
9.482⫻ 10–4 1.356 0.7376 Joint units:
watt-hours (Wh) kilowatt-hours (kWh)
103Wh = 1 kWh
J Btu
J ft-lbf
J kWh ft-lbf
3.6⫻ 106 0.2778⫻ 10–6
0.3776⫻ 10–6 2.665⫻ 106
ergs per second
horsepower (metric) (HP)
1 HP (metric) = 75 kg-m/s
POWER
foot-pounds force per second (ft-lbf/s) horsepower (British) (hp)
1 hp (British) = 550 ft-lbf/s Joint units:
watt (W) [1 W = 1 J /s 10 7 ergs/s]
kilowatt (kW)
HP (metric) kW hp (British)
1.360 0.7355
0.7457 1.341
dyne-centimeter (dyn-cm) newton-meter (N-m)
107 dyn-cm = 1 N-m
TORQUE
inch-pounds force (in.-lbf) foot-pounds force (ft-lbf)
12 in. lbf = 1 ft-lbf
1.356 0.7376
N-m ft-lbf
